1. Field of the Invention
The present invention is direct to intervertebral implants, so-called cages, with an inner channel-type structure.
2. Description of the Relevant Art
In the prior art solid and hollow implants are known in particular in the area of the spine, which either prevent the ingrowth of bone cells due to their solid structure or have a cavity which is too large to be completely filled with endogenous bone cells within a reasonable time and therefore are usually filled artificially with a bone substitute material or bone chips.
The aim of a fusion is the formation of bones, for instance by cages in the spine area, to achieve a as long as possible a stability. The growth of the bones through the implant is insofar advantageous that the bone cells can renew themselves, like elsewhere in the body and thus guarantee a long-term stability. The cages thus serve as a temporary placeholder so that the intervertebral disc space does not sink in, and thus loses height. Therefore, the cages primarily have to take over static functions, at least until the formation of bones through the implant has taken place. A quick and stable growth of bones through an artificial intervertebral implant, such as a cage, is principally desired, because such implants come closest to the natural intervertebral disc and represent the most advantageous embodiment for the patient.
The disadvantage of a solid implant such as a solid cage is obviously that a growth of bones through the implant is not possible, i.e. the implant must permanently take on the supportive function and thus is less effective in the long-term. If an implant is used as a pure spacer, there is further the risk that the implant sinks into the bone and the desired distance is no longer guaranteed. Such drawbacks could be avoided for example, that the bones grow through the implant naturally.
Hollow implants, such as hollow cages are used with or without bone replacement material. These implants, however, have the disadvantage that the bones would have to fill a large cavity, if no bone replacement material is used to fill the implants and therefore the implant would have to take on the supportive function for too long with the above-described disadvantages. If bone replacement materials are used, they serve to stimulate the growth of bones. Since blood is the catalyst for the formation of bone but the inner cavity of the cage is filled with bone replacement material and is therefore not sufficiently supplied with blood, a natural growth of bones through the partly with bone replacement material filled cage is insufficient. This in turn means that a growth of bones through a cage partly filled with bone replacement material does also not take place in the desired manner.
Therefore, it would be ideal to have a bioresorbable artificial intervertebral disc, which takes over the support function as long as the endogenous bones have replaced it and can take over the support functions. Such embodiments have not been realized previously due to a lack of suitable materials. One reason for this is the fact that no biodegradable materials are available, which ensure sufficient stability while the bone is building up, and the rate of degradation can also not be regulated sufficiently accurate, because the formation of the bone and the resorption of the implant must occur exactly at the same speed so that no transition structure is formed, which could collapse.
However, bone-joining or bone-bridging implants would be desirable, which on the one hand provide a sufficient mechanical stability and on the other hand can be grown through as completely as possible with endogenous bones.